1. Field of the Invention
The present invention relates to an image forming apparatus such as copiers, printers, facsimile machines and the like, and more particularly to an image forming apparatus having a mechanism that supplies a lubricant to the surface of an image carrier.
2. Discussion of the Background
Currently, an electrophotographic image forming apparatus as shown in FIG. 43 is used as copiers, printers and facsimile machines. In FIG. 43, a charging roller 122, an exposing unit 124, a developing unit 126, an image transfer unit 128, a cleaning blade 130 which serve as a cleaning device, and a discharger 132 are disposed around a photoconductor 120 which serves as an image carrier. Images are formed by the following processes:
(1) charging the photoconductor 120 with the charging roller 122 (charging process); PA1 (2) imagewise irradiating the photoconductor 120 with light to form electrostatic latent images thereon (exposing process); PA1 (3) developing the latent images with the developing unit 126 including a toner to form toner images on the photoconductor 120 (developing process); PA1 (4) transferring the toner images with the image transfer unit 128, for example, onto a receiving paper P which is timely fed to an image transfer position with a pair of registration rollers 134 (image transfer process); PA1 (5) feeding the receiving paper P to a fixing unit (not shown) to fix the toner images upon application of heat and pressure (image fixing process); and PA1 (6) scraping a toner remaining on the photoconductor 120 with the cleaning blade 130, and discharging the photoconductor 120 with the discharger 132, to allow the photoconductor 120 to be ready for the next cycle of these image forming processes (cleaning and discharging process). These processes are performed while the photoconductor 120 is rotated in a direction shown by an arrow. PA1 (1) abrasion caused by shear strength generated between the cleaning blade 130 and the photoconductor 120; and PA1 (2) abrasion caused by the abrasive effects of the toner which is sandwiched between the cleaning blade 130 and the photoconductor 120 and which works like a whetstone. PA1 (1) mechanical strength of the photoconductor 120; PA1 (2) pressure of contact of the cleaning blade 130 with the photoconductor 120; PA1 (3) composition of the toner; PA1 (4) coefficient of friction of the photoconductor 120; and the like. PA1 (1) toner adheres in the background part of toner images formed on the photoconductor 120, resulting in background fouling of the transferred images; and PA1 (2) the quantity of toner of character toner images formed on the photoconductor 120, resulting in deterioration of image qualities of character images. PA1 (1) small particles included in a toner tend to adhere to the photoconductor 120, resulting in background fouling or formation of a toner layer on the photoconductor 120 (referred to as a toner filming problem), and thereby image qualities deteriorate; and PA1 (2) the cleaning blade 130 tends to be turned up because the photoconductor 120 has an insufficient coefficient of friction, resulting in poor cleaning effect, and thereby fouling occurs in the background of toner images.
Among these members in the image forming apparatus as shown in FIG. 43, the charging roller 122, the image transfer unit 128, the cleaning blade 130 etc., directly contact the surface of the photoconductor 120. When the photoconductive layer of the photoconductor 120 is abraded in a certain amount with these members, the electric characteristics and photosensitive characteristics of the photoconductor 120 change, and thereby image qualities deteriorate when the predetermined image forming conditions are maintained. Thus, the abrasion of the photoconductive layer shortens the life of the photoconductor 120.
Among the members which directly contact the surface of the photoconductor 120, the cleaning blade 130 abrades the photoconductor 120 more seriously than the other members. This is because the cleaning blade 130 dynamically contacts, i.e., scrapingly contacts, the surface of the photoconductor 120 to clean the toner remaining thereon.
The abrasion of the photoconductor 120 caused by the cleaning blade 130 is broadly classified into the following two types:
The abrasion of the photoconductor 120 is determined depending on various factors which are as follows:
In attempting to decrease the abrasion of the photoconductor 120, which is caused by the contact of the cleaning blade 130, Japanese Laid-Open Patent Publications Nos. 6-324603 and 6-324604 have disclosed methods in which a lubricant is supplied to the surface of the photoconductor 120. In these methods, a lubricant supplying device 136 is used as shown in FIGS. 43 and 44.
The lubricant supplying device 136 mainly consists of a case 138 which is fixed to a main body of the apparatus, a lubricant 140 which is movably contained in the case 138, a lubricant supplying roller 142 which contacts the lubricant 140 to shave the lubricant 140, and a lubricant supplying brush 144 which takes the shaved lubricant 140 from the lubricant supplying roller 142 and supplies the lubricant 140 to the surface of the photoconductor 120. The lubricant 140 is forced to be pressed to the lubricant supplying roller 142 with springs 146, and therefore almost all the lubricant 140 can be exhausted by being applied little by little to the lubricant supplying roller 142. The thickness of the lubricant 140 decreases with elapse of time, however, the lubricant 140 always contacts the supplying roller 142 because of being pressed thereto with springs 146. As shown in FIG. 44, the lubricant 140 is shaped like a rectangular prism and is placed so as to be parallel to the longitudinal direction of the photoconductor 120. The case 138 shown in FIG. 43 has a shape corresponding to the shape of the lubricant 140 and therefore the lubricant 140 can smoothly move therethrough.
When the lubricant 140 is applied onto the surface of the photoconductor 120, the coefficient of friction between the cleaning blade 130 and the photoconductor 120 decreases, resulting in decrease of the shear strength generated therebetween, and thereby the abrasion of the photoconductor 120 can be decreased. Solid lubricants such as zinc stearate are used as the lubricant 140.
As shown in FIG. 45, Japanese Laid-Open Patent Publication No. 6-324604 discloses a lubricant supplying device 136 without a supplying roller 142 in which the lubricant 140 is applied to the surface of the photoconductor 120 with the supplying brush 144. The lubricant is contained in a case 138 and pressed with a spring 146.
Japanese Laid-Open Patent Publication No. 7-295451 discloses a technique in which a layer of a lubricant is uniformly formed on a roller using a scraper.
In addition, Japanese Laid-Open Patent Publication No. 8-54807 discloses a technique in which a roller on which a layer of a solid lubricant such as zinc stearate is formed is directly brought into contact with an image carrier to avoid formation of an uneven layer of the lubricant on the image carrier, which is caused by uneven abrasion of the solid lubricant.
Further, Japanese Laid-Open Patent Publication No. 8-95455 discloses a technique in which a solid lubricant such as waxes and metal salts of fatty acids is applied to an image carrier by means of a supplying member.
Furthermore, Japanese Laid-Open Patent Publication No. 4-264482 discloses a technique in which a counter-contact-type cleaning blade in which a layer of a polytetrafluoroethylene (hereinafter referred to as PTFE) resin is formed on the surface of the blade to be contacted with an image carrier is provided to decrease the abrasion of the image carrier.
Referring again to FIG. 43, in such lubricant supplying methods, it is preferable to supply the lubricant 140 to the photoconductor 120 as soon as possible when the lubricant 140 is desired to be supplied thereto, in order to prevent the photoconductor 120 from abrading. Namely, the lubricant 140 is preferably shaved easily with the lubricant supplying roller 142 so as to be rapidly supplied to the photoconductor 120.
In addition, when the lubricant 140 is applied to the photoconductor 120 in an excess amount, the following problems tend to occur:
In contrast, when the lubricant 140 is applied to the photoconductor 120 in an insufficient amount, the following problems tend to occur:
However, there is no satisfactory image forming apparatus nor image forming method in these points of view.
Because of these reasons, a need exists for an image forming apparatus which can stably produce good images, even when used for a long time, by allowing the surface of an image carrier to keep proper frictional properties.